The present invention relates to the stimulation of regions of a patient's brain for therapeutic purposes and, in particular, to a therapeutic brain stimulation system, a method of mounting such system relative to or on the patient's cranium, a method of adjusting the system once it has been mounted on the patients head and a therapeutic method of stimulating the brain using such system.
It is known to stimulate the human brain electrically by advancing electrodes into a specific brain region to be stimulated. In micro stimulation therapy, extremely fine glass pipettes are used. These methods are highly invasive.
It is also known to stimulate the brain with light irradiation. In this method, specific DNA fragments are introduced in the cell walls of neurons within the brain. The DNA fragments are adapted to produce light-sensitive proteins. Those neurons expressing such protein are stimulated by illumination. Illumination is carried out through a glass plate covering a surgically created hole in the patent's cranium. Thus, in this method the cranium is permanently open to allow light to be transmitted. Only outer brain areas can be stimulated by the illumination.
Furthermore, a non-invasive therapeutic brain stimulation method is known which is called “transcranial magnetic stimulation” (TMS). In this method, a circular or figure-eight type coil is used to create an electromagnetic field inside the brain, thereby inducing a current in the brain's neurons, in particular in those neurons having the axons parallel to the electric field. The position and orientation of the coil as well as the duration and intensity of stimulation can be varied. In so-called repetitive TMS (rTMS) a sequence of stimulus pulses is provided, the pulse length, the time between the pulses, the duration of the stimulation sequence and the number of stimulation sequences being varied to achieve different therapeutic results. A plurality of coils can be used to stimulate different brain regions to achieve a combinatory therapeutic effect. However, as the distance to the coil increases linearly, the intensity of the electromagnetic field decreases exponentially. Also, the heat dissipation close to the patient's head can cause problems. The application of TMS and rTMS is thus limited to the outer areas of the brain, i.e. to the cerebral cortex, in proximity to the parietal and occipital cranial bone structure.
It is further known, but not in the context of brain stimulation, to subject the human brain to ultrasonic waves. The ultrasonic waves are applied to destroy brain tumours by non-invasive surgery. A complex network of a great number of small ultrasound emitters, such as more than 300 senders, are applied to the patient's head from the outside thereof and directed towards a very limited target area of e.g. 1 mm in size within the patient's brain. The little size and equal distribution prevents regions of the brain outside the target area from heating up above a critical cell temperature. However, where the destroyed tumour cells cannot be removed by internal body functions, the cranium has nevertheless to be opened for removing the dead tumour cells, unlike related methods of destroying kidney stones where the fragments of the ultrasonically destroyed stones are discarded naturally.
Alternatively, the target can be irradiated stereo-tactically (DE 196 14 643 A1). In this method, the patient and/or an irradiation source are rotated relative to a target centre within the patient's brain. This way, the target is hit from different sides over time, the radiation ultimately leading to the destruction of the tumour cells.